The invention relates to a method for splicing optical conductors by using an arc discharge between two electrodes and controlling the arc discharge by controlling the discharge current and to a splicing device which has two electrodes, holding devices for positioning the conductors between the electrodes, a current source for striking an arc discharge between the electrodes and a set point generator for providing a preset discharge current for the source.
Two methods are known for connecting the optical conductors (glass or polymer fibers) which are being increasingly used in optical telecommunications engineering: on the one hand, bonding ends of the optical conductors in preassembled and standardized connectors and, on the other hand, splicing optical conductors with prepared end faces to form a single optical conductor. When splicing the optical conductors in splicing devices, two optical conductors with prepared end faces are fastened on two holding devices which can then be moved with the aid of adjusting devices so that the end faces are well adjusted relative to one another. After the adjustment, the two ends are then, in general, thermally welded. The thermal welding is performed in this case using an arc discharge between two electrodes.
U.S. Pat. No. 4,506,947 discloses a method in which a video camera is used to adjust two glass fibers relative to one another in a controlled fashion by illuminating the splice point with ultraviolet light so that the core of the glass fibers, which is doped with germanium, emits light in the visible wavelength region. The light is displayed on a monitor via the video camera and a downstream image evaluation unit. The operator of the device can therefore adjust the cores of the two glass fibers relative to one another via the monitoring device and the adjusting device. The quality of the splicing operation is not observed.
The quality of a splice which is intended to achieve optical losses as small as possible during the transmission of light from one optical conductor into the other, depends essentially on the parameters set in the splicing device. The discharge current used to weld the optical conductors is also one of these parameters. In the case of optimum adjustment and constant ambient conditions (air pressure, air humidity, temperature), heating which remains good is achieved with the aid of a constant discharge current. In the case of altered ambient conditions and used or soiled electrodes, there is a change in the heating of the optical conductors even given a constant discharge current, and thus a change in the quality of splicing.
In the field of material processing of work pieces using lasers, DE 196 17 388 discloses a method which uses video sensors to evaluate the temperature distribution in a plasma initiated by a laser. The plasma corresponds to the arc discharge during splicing, but the method can provide no information either on the temperature distribution in the optical conductor itself, or thus on the quality of the splice.
It is therefore the object of the invention to automate the control of the temperature for a splicing operation independently of ambient parameters.
The object is achieved by means of a method and a splicing device of the type mentioned at the beginning by using a sensor to measure the actual intensity distribution occurring during splicing, storing a reference intensity distribution in a storage device, comparing the measured intensity distribution with the reference intensity distribution and correcting the discharge current in a controller in response to any deviations therebetween.
For this purpose, the actual intensity distribution occurring in the case of optical conductors which emit thermionically upon the application of a preset discharge current is measured and compared with a stored reference intensity distribution. Intensity distribution is understood below as a spatially resolved (if appropriate, also wavelength-resolved) image of the ends of the optical conductors. In the case of a deviation, the discharge current is then varied such that the actual intensity distribution attained at least approaches the stored reference intensity distribution. This results in automated control of the discharge current which is independent of ambient parameters, and so splicing operations lead to identical temperature distributions in the optical conductors, and thus to a quality of the splices which remains good.
The newly determined, adapted discharge current is advantageously stored as a preset discharge current for future splicing operations.
When color cameras are used, the reference intensity distribution can be stored in a wavelength-resolved fashion and compared with wavelength-resolved actual intensity distributions during the splicing operations in order to arrive at a more accurate statement on the temperature distribution in the optical conductors.
When black and white cameras are used gray-scale values are advantageously assigned to the intensity distributions.
The gray-scale values determined in the process are averaged over the area of the two optical conductors, and only this mean gray-scale value of the actual intensity distribution is compared with a mean reference gray-scale value. The quantity of data to be stored is advantageously reduced by this process.
In a preferred embodiment, the gray-scale values of a row of the optical sensor are evaluated in the direction of the axes of the two optical conductors in a spatially resolved fashion. The actual position of a prescribed gray-scale value which occurs is compared with a stored reference position of the prescribed gray-scale value, and in the case of a deviation the discharge current is corrected such that the actual position approaches the reference position. The quantity of data to be stored is also reduced by this embodiment.
A temporal actual sequence of intensity distributions is advantageously stored and compared with a stored reference sequence in order to arrive at a yet more accurate statement on the temperature distribution during the splicing operation.
A particularly reproducible method is achieved by virtue of the fact that the temporal sequence is triggered by the application of the discharge current.
In the case of the splicing device, a memory is provided for storing the reference intensity distribution in order thereby to compare in a comparator the actual intensity distribution measured with the aid of a sensor. A controller serves the purpose of controlling the discharge current as a function of the comparison made.
For the purpose of a simple construction in conjunction with reduced costs, the sensor is designed such that it can also be used to adjust the ends of the optical conductors.
The invention is explained in more detail in exemplary embodiments with the aid of the figures of the drawins.